UV Absorbance Spectroscopy of Biological Macromolecules

Synonyms
DNA; Protein absorbance spectroscopy; RNA

Definition
Proteins, DNAs and RNAs are linear polymers where a limited set of residues are joined together by, respectively, the amide or phosphodiester bonds. The situation is similar for carbohydrates though the linking options are more varied here. To a first approximation, the absorbance spectrum expected for a biomolecule is the sum of the component parts. However, the polymerization process and the packing of the units perturb the spectra as discussed below (Berova et al. in press; Nordén and Rodger 2010; Wallace and Janes 2009).

Basic Characteristics
Electronic Spectroscopy of Nucleic Acid Bases
The absorption spectra of nucleic acids in the easily accessible region of the spectrum (down to ∼180 nm) are dominated by π → π* transitions, which are, by symmetry, all polarized in the plane of the bases, so approximately perpendicular to the helix axis in B-DNA. The absorbance spectra of the DNA bases thymine (T), adenine (A),...